1. Field of the Invention
The present invention relates to a control method for an automatic transmission of an engine-driven vehicle.
2. Background
Automatic transmissions for vehicles are known in which an electronic control unit generates signals for the control of a plurality of actuators (for instance of hydraulic type) which are coupled to a gear change and to a clutch and are used to cause the selection and engagement/disengagement of the gears and to cause the opening/closure of the clutch.
According to an automatic operating method, the control unit receives as input a plurality of data signals (vehicle speed, accelerator pedal position, revolutions per minute, torque supplied by the engine, etc.) which are processed to detect the most appropriate situations in which to perform a gear change, in particular an increment (UP-SHIFT) of the gear engaged or a decrement (DOWN-SHIFT) of the gear engaged.
These control units may also operate according to a manual operating method in which an operator acts on a control member (for instance of the lever type) in order to command the selection and engagement of the gears, in particular to perform a unit increment of the transmission ratio engaged or a unit decrement of the transmission ratio engaged.
Automatic transmissions are also known which provide for both of the above-mentioned operating methods (manual/automatic); these operating methods are mutually exclusive and the desired operating method is selected by a command from the operator.
Some automatic transmissions are, for instance, provided with a control lever which can be disposed in a first stable position for the actuation of the automatic operating method and in a second stable position which controls the engagement of the manual operating method; the operator may also displace the lever disposed in the second position in opposite directions in order to carry out unit increments/decrements of the gear engaged.
In other automatic transmissions operating by lever control, the lever may be disposed in a single position for the engagement of the manual operating method; here again, the operator can displace the lever disposed in the stable position in opposite directions in order to perform unit increments/decrements of the gear engaged. The automatic operating method is selected by actuating a dedicated switch, in particular a push-button switch.
In particular circumstances, the strategies for the choice of the transmission ratio engaged in the automatic method may not coincide with the choice that the driver would make. In such circumstances, it is advantageous for the operator to be able to modify the gear that has been selected and engaged in a fully automatic manner.
In known systems, in the above-mentioned circumstances, the driver may modify the gear in use only by exiting from the automatic operating method. This operation may be inconvenient for the operator.